There has been a marked increase in first births among women age 30 or more in th U.S. and the numbers have increased from 1975 to 1986 from 69,000 to 230,000 per year. There is a controversy as to whether there is an increased risk of adverse birth outcome among delayed childbearers. There is also a question whether reported increase risk in adverse birth outcome is due to confounding by other factors. This research is using a population based Swedish data set of more than 500,00 births from 1983 to 1987, which in addition to demographic characteristics include information on medical and pregnancy complications, history of infertility reproductive history, as well as smoking. This is a unique data set and we are aware of any comparable population based information in the United States. Several manuscripts have been developed and submitted and two are currently in press.